Section 3

Question 1

digestion of starch

Answer 1

• amylase hydrolyses glycosidic bonds in starch to produce maltose
• maltase hydrolyses glycosidic bonds in maltose to produce glucose

Question 2

digestion of proteins

Answer 2

• endopeptidases hydrolyse peptide bonds in the middle of the polypeptide chain
• exopeptidases hydrolyse peptide bonds at the end of the polypeptide chain
• endopeptidases create more ends for exopeptidases to act on
• depeptidases hydrolyse peptide bonds in dipeptides to release single amino acids

Question 3

digestion of lipids + what happens before lipids are digested

Answer 3

before: large lipid globules are emulsified into smaller lipid droplets by bile salts which increase the surface area for lipase to act on
digestion: lipase hydrolyses ester bonds in triglycerides and produces monoglycerides and fatty acids (arranged into micelles, which make them more soluble, contain fatty acids, monoglycerides and bile salts)

Question 4

mechanism in the lungs: breathing in

Answer 4

• the diaphragm contracts and lowers/flattens. the external intercostal muscles contract, whilst the internal intercostal muscles relax. the ribs are pulled up and out
• this increases the volume of the lungs/thorax and decreases the pressure below atmospheric pressure
• air is drawn into the lungs down the pressure gradient

Question 5

mechanism in the lungs: breathing out

Answer 5

• the diaphragm relaxes and moves to a higher, domed position. the internal intercostal muscles contract, whilst the external intercostal muscles relax. this pulls ribs down and in
• this decreases the volume of the lungs/thorax and increases the pressure above atmospheric pressure
• air is forced out of the lungs down the pressure gradient

Question 6

fat absorption

Answer 6

1. fatty acids and monogylcerides arrive at epithelial cells lining the ileum arranged into micelles
2. induvidual fatty acids and monoglycerides diffuse across the membrane into the epithelial cell
3. fatty acids and monoglycerides reformed into triglycerides in the smooth endoplasmic reticulum
4. triglycerides are modified in the golgi body by adding protein and cholesterol to form chylomicrons
5. chylomicrons exit the base of the epithelial cell via exocytosis and enter lymphatic capillaries/lacteal
6. they are returned to the blood stream much later